Surface emitting laser, manufacturing method of surface emitting laser, surface emitting laser array, manufacturing method of surface emitting laser array, and optical apparatus including surface emitting laser array

ABSTRACT

A surface emitting laser which is configured by laminating on a substrate a lower reflection mirror, an active layer, and an upper reflection mirror, which includes, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, wherein the upper reflection mirror is configured by a multilayer film reflection mirror based on a laminated structure formed by laminating a plurality of layers, the multilayer film reflection mirror includes a phase adjusting layer which has an optical thickness in the range of λ/8 to 3λ/8 inclusive in a light emitting peripheral portion on the multilayer film reflection mirror, and an absorption layer causing band-to-band absorption is provided in the phase adjusting layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface emitting laser, amanufacturing method of the surface emitting laser, a surface emittinglaser array, a manufacturing method of the surface emitting laser array,and an optical apparatus including the surface emitting laser array.

2. Description of the Related Art

As one of the surface emitting lasers, there is known a vertical cavitysurface emitting laser (hereinafter referred to as VCSEL).

According to the surface emitting laser of this type, a light beam canbe taken out perpendicularly to a semiconductor substrate surface, andhence a two-dimensional array can be easily formed only by changing amask pattern at the time of forming the laser elements.

The parallel processing using the plurality of beams emitted from thetwo-dimensional array enables the increase in density and speed, andhence is expected to be applied in various industrial fields.

For example, when the surface emitting laser array is used as anexposure light source of an electrophotographic printer, it is possibleto increase the density and speed in the printing process by using theplurality of beams.

In such electrophotographic printing process, it is necessary to formstable and minute laser spots on a photosensitive drum. Thus, a stableoperation in a single transverse mode or a single longitudinal mode isalso required as a laser characteristic.

In recent years, there has been developed a method in which a currentconstriction structure is formed so as to allow current to be injectedonly into a necessary region.

In this method, in order to enhance the performance of the surfaceemitting laser, current is allowed to be injected only into a necessaryregion by forming the current constriction structure in such a mannerthat a layer having a high Al composition, for example, an AlGaAs layerhaving an Al composition of 98% is formed in a multilayer filmreflection mirror and selectively oxidized in a high temperature steamatmosphere.

Meanwhile, the above described method using selective oxidization is notdesirable from the viewpoint of realizing a single transverse modeoscillation.

That is, a refractive index difference which is larger than needed iscaused due to the existence of the oxidized layer, so that high ordertransverse modes are generated.

As a method to cope with this problem, there is used a method, and thelike, in which a single transverse mode oscillation is achieved in sucha manner that the diameter of the light emitting region is reduced toabout 3 μm by using the above described current constriction structureso as to prevent the high order transverse modes from being confined.

However, in the method of restricting the light emitting region, thelight emitting region is reduced, and thereby the output per element issignificantly reduced.

For this reason, heretofore, there have been investigated methods forrealizing a single transverse mode oscillation while maintaining a lightemitting region which is larger to some extent than the region obtainedin the case where the single transverse mode oscillation is realizedonly by reducing the light emitting region by using the above describedcurrent constriction structure.

That is, there have been investigated methods in which a singletransverse mode oscillation can be realized by intentionally introducinga loss difference between a fundamental transverse mode and a high ordertransverse mode, while maintaining a light emitting region that is largeto some extent.

As one of the methods, a so-called surface relief method is disclosed inJapanese Patent Application Laid-Open No. 2001-284722, H. J. Unold etal., Electronics Letters, Vol. 37, No. 9 (2001) 570, and J. A. Vukusicet al., IEEE JOURNAL OF QUANTUM ELECTRONICS, Vol. 37, No. 1, 2001 (108).

The surface relief method is a method in which the loss in the highorder transverse mode is increased to be larger than the loss in thefundamental transverse mode by applying level difference processing tothe element surface which is the light emitting surface of the surfaceemitting laser element.

Note that in the present specification, it is assumed that, in thefollowing, the level difference structure, which is provided, asdescribed above, in the light emitting region of the light emittingsurface of the reflection mirror to control the reflectance of thereflection mirror, is referred to as a surface relief structure.

Generally, as a mirror for the VCSEL, there is used a multilayer filmreflection mirror in which a plurality of pairs of layers, each of whichhas a different refractive index and an optical thickness of one fourthof a laser oscillation wavelength (that hereinafter may be referred toas ¼ wavelength unless otherwise specified), are laminated so that thetwo layers are alternately arranged.

Usually, the multilayer film reflection mirror is terminated by a highrefractive index layer, so that a high reflectance of 99% or more isobtained by also using the reflection on the final interface with airhaving a low refractive index.

First, the concave surface relief structure shown in FIG. 2A isdescribed hereinbelow.

Such concave surface relief structure is also disclosed in JapanesePatent Application Laid-Open No. 2001-284722.

In a low reflection region 204 shown in FIG. 2A, a low refractive indexlayer 208 (or which may be a high refractive index layer) is furtheradded to the final layer of a high refractive index layer 206.

Thereby, there is obtained a concave surface relief structure in whichthe multilayer film reflection mirror is terminated so as to have thethickness thereof being increased by an optical thickness of ¼wavelength.

According to such concave surface relief structure, the phase of a lightbeam reflected by the interface between the final layer of themultilayer film reflection mirror, here, the low refractive index layer208, and the air having a further lower refractive index is shifted by πfrom the phase of the light beam which is totally reflected by themultilayer film reflection mirror and which exists under the interface.

For this reason, in the low reflection region 204, the reflectance isreduced to 99% or less, so that the reflection loss can be increased toabout 5 to 15 times.

In order to introduce a loss difference between the basic transversemode and the high order transverse mode by using this principle, the lowreflection region 204 is formed only in the light emitting peripheralportion so as to increase the overlap between the low reflection region204 and the high order transverse mode light distribution 212.

On the other hand, the high reflection region 202 is left in the lightemitting central portion so as to increase the overlap between the basictransverse mode light distribution 210 and the high reflection region202 having the high refractive index layer 206 as the final layer.

Thereby, the reflection loss is increased in the high order transversemode, so that the oscillation in the high order transverse mode can besuppressed and only the oscillation of basic transverse mode can beobtained. In this case, as shown in FIG. 2A, a concave shape is formedas the relief shape.

Further, it is also possible to configure a convex surface reliefstructure in such a manner that as in the low reflection region 204illustrated in FIG. 2B, the final layer of the high refractive indexlayer 206 is removed and that the multilayer film reflection mirror isterminated by the low refractive index layer 208.

Such convex surface relief structure is also disclosed in H. J. Unold etal., Electronics Letters, Vol. 37, No. 9 (2001) 570. Even by suchconfiguration, the reflectance can be reduced based on the sameprinciple as the concave shape, so that the fundamental transverse modeoscillation can be effected.

According to the above described surface relief structure in the priorart form disclosed in Patent Japanese Patent Application Laid-Open No.2001-284722, and H. J. Unold et al., Electronics Letters, Vol. 37, No. 9(2001) 570 and J. A. Vukusic et al., IEEE JOURNAL OF QUANTUMELECTRONICS, Vol. 37, No. 1, 2001 (108), a single transverse modeoscillation can be realized while the light emitting region ismaintained to be larger to some extent than the light emitting regionobtained in the case where the single transverse mode is realized onlyby the current constriction structure.

However, the reflectance in the surface relief structure is sensitivelyinfluenced by the thickness of layers forming the surface reliefstructure, and has a great influence on realizing the single transversemode oscillation. Therefore, it is extremely important to control thelayer thickness in the manufacture of the surface relief structure.

That is, the surface relief structure has a feature that the reflectance(reflection loss) is very sensitive to the layer thickness removed oradded in the manufacture of the surface relief structure.

Next, there will be further described features of the above describedsurface relief structure.

FIG. 3 is a figure which is described in J. A. Vukusic et al., IEEEJOURNAL OF QUANTUM ELECTRONICS, Vol. 37, No. 1, 2001 (108) and in whichthe layer thickness removed by the surface relief is plotted along thehorizontal axis while the induced loss is plotted along the verticalaxis (left side).

From FIG. 3, there can be seen a state where the loss has peaksappearing periodically with respect to the layer thickness which isremoved.

Further, the peak is steep, and when a desired loss value is to beintroduced, the layer thickness which is removed needs to be controlledwith very high accuracy (±5 nm or less).

On the other hand, the amount of the loss greatly influences the extentto which the single mode oscillation is realized, and further greatlyinfluences the output characteristic of the element.

Therefore, in the manufacture of the surface relief structure, it isnecessary to highly precisely control the layer thickness in order tomanufacture elements which have good reproducibility and uniformity andwhich are capable of performing a single mode operation with the samecharacteristics.

In other words, it can be said that for the manufacture of the surfacerelief structure, when the thickness of the layer to be removed or addedcan be simply grasped with high accuracy and when the layer thicknesscan be adjusted according to the grasped layer thickness, thereproducibility and uniformity in the manufacture of the element can begreatly improved.

An object of the present invention is to provide a surface emittinglaser including a concave surface relief structure, the layer thicknessof which can be highly precisely controlled and which is capable ofperforming a single mode operation with good reproducibility anduniformity, and to provide a manufacturing method of the surfaceemitting laser.

A further object of the present invention is to provide a surfaceemitting laser array configured by the above described surface emittinglasers, a manufacturing method of the surface emitting laser arrayconfigured by the surface emitting lasers, which is based on the abovedescribed manufacturing method of the surface emitting laser, and anoptical apparatus including the surface emitting laser array.

SUMMARY OF THE INVENTION

The present invention is directed to a surface emitting laser which isconfigured by laminating on a substrate a lower reflection mirror, anactive layer, and an upper reflection mirror, which includes, in a lightemitting section of the upper reflection mirror, a structure forcontrolling reflectance that is configured by a low reflectance regionand a concave high reflectance region formed in the central portion ofthe low reflectance region, and which oscillates at a wavelength of λ,wherein the upper reflection mirror is configured by a multilayer filmreflection mirror based on a laminated structure formed by laminating aplurality of layers,

the multilayer film reflection mirror includes a phase adjusting layerwhich has an optical thickness in the range of λ/8 to 3λ/8 inclusive ina light emitting peripheral portion on the multilayer film reflectionmirror, and an absorption layer causing band-to-band absorption isprovided in the phase adjusting layer.

The absorption coefficient of the absorption layer can be set to 5000cm⁻¹ or more for the wavelength λ.

The absorption layer can be arranged at a layer positioned at the middlepoint in a thickness direction of the phase adjusting layer, or arrangedon the surface side from the layer positioned at the middle point in thethickness direction of the phase adjusting layer.

The present invention is directed to an optical apparatus comprising, asa light source, a surface emitting laser array configured by arranging aplurality of the surface emitting lasers.

The present invention is directed to a surface emitting laser which isconfigured by laminating on a substrate a lower reflection mirror, anactive layer, and an upper reflection mirror, which includes, in a lightemitting section of the upper reflection mirror, a structure forcontrolling reflectance that is configured by a low reflectance regionand a concave high reflectance region formed in the central portion ofthe low reflectance region, and which oscillates at a wavelength of λ,wherein the upper reflection mirror is configured by a multilayer filmreflection mirror based on a laminated structure formed by laminating aplurality of layers, the multilayer film reflection mirror includes aphase adjusting layer which has an optical thickness in the range of λ/8to 3λ/8 in a light emitting peripheral portion on the multilayer filmreflection mirror, and an absorption layer causing band-to-bandabsorption is provided on the surface side from a layer laminated at themiddle point in thickness of the laminated structure that configures themultilayer film reflection mirror.

The absorption coefficient of the absorption layer can be 5000 cm⁻¹ ormore for the wavelength λ.

The absorption layer can be provided within five pairs of layers fromthe surface side of the laminated structure.

The absorption layer can be arranged so that when seen from the surfaceside of the multilayer film reflection mirror, a part of the absorptionlayer is included in the interface from a high refractive index layer toa low refractive index layer in the multilayer film reflection mirror.

The present invention is directed to an optical apparatus comprising, asa light source, a surface emitting laser array configured by arranging aplurality of the surface emitting lasers.

The present invention is directed to a surface emitting laser which isconfigured by laminating on a substrate a lower reflection mirror, anactive layer, and an upper reflection mirror, which includes, in a lightemitting section of the upper reflection mirror, a structure forcontrolling reflectance that is configured by a low reflectance regionand a concave high reflectance region formed in the central portion ofthe low reflectance region, and which oscillates at a wavelength of λ,wherein the upper reflection mirror is configured by a multilayer filmreflection mirror based on a laminated structure formed by laminating aplurality of layers,

the multilayer film reflection mirror includes a phase adjusting layerwhich has an optical thickness in the range of λ/8 to 3λ/8 in a lightemitting peripheral portion on the multilayer film reflection mirror,and an absorption layer having an absorption coefficient of 5000 cm⁻¹ ormore for the wavelength λ is provided in the phase adjusting layer.

The present invention is directed to a surface emitting laser which isconfigured by laminating on a substrate a lower reflection mirror, anactive layer, and an upper reflection mirror, which includes, in a lightemitting section of the upper reflection mirror, a structure forcontrolling reflectance that is configured by a low reflectance regionand a concave high reflectance region formed in the central portion ofthe low reflectance region, and which oscillates at a wavelength of λ,wherein the upper reflection mirror is configured by a multilayer filmreflection mirror based on a laminated structure formed by laminating aplurality of layers,

the multilayer film reflection mirror includes a phase adjusting layerwhich has an optical thickness in the range of λ/8 to 3λ/8 in a lightemitting peripheral portion on the multilayer film reflection mirror,and an absorption layer having an absorption coefficient of 5000 cm⁻¹ ormore for the wavelength λ is provided on the surface side from a layerlaminated at the middle point in thickness of the laminated structurethat configures the multilayer film reflection mirror.

The present invention is directed to a manufacturing method of a surfaceemitting laser in which a lower reflection mirror, an active layer, andan upper reflection mirror are successively laminated on a substrate, inwhich there is formed, in a light emitting section of the upperreflection mirror, a structure for controlling reflectance that isconfigured by a low reflectance region and a concave high reflectanceregion formed in the central portion of the low reflectance region, andwhich oscillates at a wavelength of λ, the manufacturing methodcomprising: forming, as the upper reflection mirror, a multilayer filmreflection mirror based on a laminated structure; forming, on themultilayer film reflection mirror, a phase adjusting layer which is forreducing the reflectance and which includes an absorption layer causingband-to-band absorption; measuring reflection spectra by irradiating thesurface of the phase adjusting layer with light;

measuring a broad dip wavelength obtained by measuring the reflectionspectra; and adjusting the thickness of the phase adjusting layer basedon the dip wavelength.

The absorption coefficient of the absorption layer can be set to 5000cm⁻¹ or more for the wavelength λ.

The manufacturing method of the surface emitting laser can furthercomprise forming, when the absorption layer is formed, the absorptionlayer at a layer positioned at the middle point in a thickness directionof the phase adjusting layer, or on the surface side from the layerpositioned at the middle point in the thickness direction of the phaseadjusting layer.

The present invention is directed to a manufacturing method of a surfaceemitting laser in which a lower reflection mirror, an active layer, andan upper reflection mirror are successively laminated on a substrate,

in which there is formed, in a light emitting section of the upperreflection mirror, a structure for controlling reflectance that isconfigured by a low reflectance region and a concave high reflectanceregion formed in the central portion of the low reflectance region, andwhich oscillates at a wavelength of λ, the manufacturing methodcomprising: forming, when a multilayer film reflection mirror based on alaminated structure is formed as the upper reflection mirror, anabsorption layer causing band-to-band absorption on the surface side inthe laminated structure from a layer laminated at the middle point inthickness of the laminated structure; measuring reflection spectra byirradiating the laminated structure with light; measuring a broad dipwavelength obtained by measuring the reflection spectra; forming, afterthe multilayer film reflection mirror as the upper reflection mirror isformed, a phase adjusting layer for reducing reflectance on themultilayer film reflection mirror; and adjusting the thickness of thephase adjusting layer based on the dip wavelength.

The absorption coefficient of the absorption layer can be set to 5000cm⁻¹ or more for the wavelength λ.

The manufacturing method of the surface emitting laser can furthercomprises forming, when the absorption layer is formed, the absorptionlayer within five pairs of layers from the surface side of the laminatedstructure.

The manufacturing method of the surface emitting laser can furthercomprise forming, when the absorption layer is formed, the absorptionlayer so that when seen from the surface side of the multilayer filmreflection mirror, a part of the absorption layer is included in theinterface from a high refractive index layer to a low refractive indexlayer in the multilayer film reflection mirror.

The manufacturing method of the surface emitting laser can furthercomprise forming, when the absorption layer is formed, the absorptionlayer so that the thickness of the absorption layer is set to 2 nm ormore to 30 nm or less.

The present invention is directed to a manufacturing method of a surfaceemitting laser in which a lower reflection mirror, an active layer, andan upper reflection mirror are successively laminated on a substrate, inwhich there is formed, in a light emitting section of the upperreflection mirror, a structure for controlling reflectance that isconfigured by a low reflectance region and a concave high reflectanceregion formed in the central portion of the low reflectance region, andwhich oscillates at a wavelength of λ, the manufacturing methodcomprising: forming, as the upper reflection mirror, a multilayer filmreflection mirror based on a laminated structure; forming, on themultilayer film reflection mirror, a phase adjusting layer which is forreducing the reflectance and which includes an absorption layer havingan absorption coefficient of 5000 cm⁻¹ or more for the wavelength λ;measuring reflection spectra by irradiating the surface of the phaseadjusting layer with light; measuring a broad dip wavelength obtained bymeasuring the reflection spectra; and adjusting the thickness of thephase adjusting layer based on the dip wavelength.

The present invention is directed to a manufacturing method of a surfaceemitting laser in which a lower reflection mirror, an active layer, andan upper reflection mirror are successively laminated on a substrate,

in which there is formed, in a light emitting section of the upperreflection mirror, a structure for controlling reflectance that isconfigured by a low reflectance region and a concave high reflectanceregion formed in the central portion of the low reflectance region, andwhich oscillates at a wavelength of λ, the manufacturing methodcomprising: forming, when a multilayer film reflection mirror based on alaminated structure is formed as the upper reflection mirror, anabsorption layer having an absorption coefficient of 5000 cm⁻¹ or morefor the wavelength λ on the surface side in the laminated structure froma layer laminated at the middle point in thickness of the laminatedstructure; measuring reflection spectra by irradiating the laminatedstructure with light; measuring a broad dip wavelength obtained bymeasuring the reflection spectra; forming, after the multilayer filmreflection mirror as the upper reflection mirror is formed, a phaseadjusting layer for reducing reflectance on the multilayer filmreflection mirror; and adjusting the thickness of the phase adjustinglayer based on the dip wavelength.

According to the present invention, it is possible to realize a surfaceemitting laser including a concave surface relief structure, the layerthickness of which can be highly precisely controlled and which iscapable of performing a single mode operation with good reproducibilityand uniformity, and it is possible to realize a manufacturing method ofthe surface emitting laser.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic view for describing a verticalcavity surface emitting laser including a concave surface reliefstructure in exemplary embodiment 1 according to the present invention,and a manufacturing method of the surface emitting laser.

FIGS. 2A and 2B are cross-sectional schematic views for describing aconcave surface relief structure (FIG. 2A) and a convex surface reliefstructure (FIG. 2B) which are used in the prior art form.

FIG. 3 is a figure for describing the layer thickness dependency of thenormalized loss introduced into a laser including the surface reliefstructure, which is a prior art form and is disclosed in Non-patentdocument 2, and is a figure obtained by plotting the layer thicknessremoved by the surface relief along the horizontal axis, and plottingthe introduced loss along the vertical axis (left side).

FIG. 4 is a cross-sectional schematic view for describing a wafer layerstructure of a surface emitting laser including a concave surface reliefstructure in an exemplary embodiment according to the present invention.

FIG. 5 is a figure for describing the difference in the dip shape due tothe difference in the absorption coefficient of the absorption layer inthe exemplary embodiment according to the present invention, andillustrating reflection spectra of the wafer layer structure of thesurface emitting laser.

FIG. 6 is a figure for describing the layer structure of the multilayerfilm reflection mirror of the surface emitting laser in the exemplaryembodiment according to the present invention, and internal lightintensity distributions at the time when the element is driven and whenthe reflection spectra are measured.

FIG. 7 is a figure for describing the layer thickness dependency of thenormalized loss introduced into the low reflection region in theexemplary embodiment according to the present invention, andillustrating the normalized loss introduced when the layer thickness ofeach of the first layer to the fourth layer is varied.

FIG. 8 is a figure for describing the dip wavelength dependency of thenormalized loss introduced into the low reflection region in theexemplary embodiment according to the present invention, andillustrating the normalized loss introduced when the layer thickness ofeach of the first layer to the fourth layer is varied.

FIG. 9 is a cross-sectional schematic view for describing a verticalcavity surface emitting laser including the concave surface reliefstructure in exemplary embodiment 2 according to the present invention,and a manufacturing method of the vertical cavity surface emittinglaser.

FIG. 10 is a figure for describing the difference in the dip wavelengthdue to the difference in the layer thickness of the surface layer in thereflection region of the exemplary embodiment according to the presentinvention, and illustrating the reflection spectra of the wafer layerstructure of the surface emitting laser.

FIGS. 11A and 11B are figures illustrating actual measurement results ofthe reflection spectra of the wafer manufactured in exemplary embodiment1 according to the present invention.

FIGS. 12A and 12B are schematic views for describing an image formingapparatus in exemplary embodiment 4 according to the present invention.

FIG. 13 is a cross-sectional schematic view for describing a verticalcavity surface emitting laser including a concave surface reliefstructure in exemplary embodiment 3 according to the present invention3, and a manufacturing method of the vertical cavity surface emittinglaser.

FIG. 14 is a figure for describing the difference in the dip shape dueto the difference in the thickness of the absorption layer in theexemplary embodiment according to the present invention, andillustrating reflection spectra of the wafer layer structure of thesurface emitting laser.

DESCRIPTION OF THE EMBODIMENTS

According to the above described configuration of the present invention,it is possible to manufacture a highly precise concave surface reliefstructure. Thereby, it is possible to provide a surface emitting laserwhich is capable of performing a single mode operation with excellentreproducibility and uniformity, and to provide a manufacturing method ofthe surface emitting laser.

This is based on the following knowledge obtained as a result of anextensive investigation by the present inventors.

The present inventors measured the reflection spectra of a wafer havingthe surface emitting laser layer structure before on element is formed.

As a result, it was found that broad dips 514 are generated as indicatedby lines 506, 508, and 510 in FIG. 5.

Then, there was found a method for quantitatively estimating the amountof introduced loss by grasping the wavelength (hereinafter referred toas dip wavelength) corresponding to the dip.

The dip wavelength reflects the thickness information of the layerforming the low reflection region in the relief structure, and theamount of introduced loss can be estimated in advance from the dipwavelength. In other words, it can be said that the layer thickness ofthe surface layer forming the low reflection region may be adjusted,that is, the layer thickness of a phase adjusting layer may adjusted soas to make the dip wavelength correspond to a desired amount of loss.

Next, the principle will be described.

FIG. 5 is a figure for describing the difference in the dip shape due tothe difference in the absorption coefficient of the absorbing layer. Inorder that the dip wavelength 514 in the low reflection region in FIG. 5can be grasped from the reflection spectrum measurement, the wafer layerstructure needs to satisfy the following conditions.

As the first condition, in order to form a low reflection region, aphase adjusting layer having an optical thickness in the range of ⅛wavelength to ⅜ wavelength inclusive is further provided on a multilayerfilm reflection mirror terminated by a high refractive index layer.

As the second condition, a layer which causes large absorption of anband-to-band absorption level (5000 cm⁻¹ or more) in the oscillationwavelength is provided in the phase adjusting layer and the multilayerfilm reflection mirror.

Here, a low reflection region of a relief structure which serves as thefirst condition corresponds to, for example, the low reflection region204 in FIG. 2A.

The layer added based on the first condition exists on the outermostsurface. The phase of light reflected by the interface between the addedlayer and the layer of air, a dielectric film, or the like, whichfurther exists above the added layer and which has a refractive indexlower than that of the added layer, is adjusted, that is, the layerthickness of the added layer is adjusted so that the light is reflectedin reverse phase by the interface, and thereby the reflectivity as awhole is reduced.

In this specification, it is assumed that this final layer is referredto as a phase adjusting layer.

FIG. 4 illustrates an example in the case of a red surface emittinglaser based on a wafer layer structure satisfying the above describedconditions. FIG. 5 illustrates examples of reflection spectra of theabove described wafer layer structure.

The reflection spectra are measured so as to cover a range from theshort wavelength side to the long wavelength side with the laseroscillation wavelength as the center.

As shown in FIG. 4, a GaAs phase adjusting layer 418 having an opticalthickness of ¼ wavelength exists on an Al_(0.5)Ga_(0.5)As highrefractive index layer 416, and the GaAs layer absorbs light having anoscillation wavelength of 680 nm by band-to-band absorption.

Therefore, two of the above described first and second conditions aresatisfied.

In this case, in the reflection spectra, there can be seen a sharpresonance wavelength 512 due to the high reflection band of themultilayer film reflection mirrors 412 and 404, and the surface emittinglaser resonator, and further a broad dip wavelength 514 in the lowreflection region can also be observed as shown by solid line 506 (inthe case of absorption coefficient of 5000 cm⁻¹ or more) in FIG. 5.

Next, there will be described a reason why the dip wavelength 514 isgenerated due to the low reflection region, that is, the phase adjustinglayer.

In the configuration according to the present exemplary embodiment,there is provided, on the normal multilayer film reflection mirror 412,a layer having an optical thickness of ¼ wavelength as the phaseadjusting layer (GaAs layer 418).

Therefore, in view of the structure which is formed by combining thephase adjusting layer and the high refractive index layer(Al_(0.5)Ga_(0.5)As high refractive index layer 416) existingimmediately below the phase adjusting layer, and which has an opticalthickness of ½ wavelength,

a reflection mirror formed by the interface between the air and the GaAslayer exists in the upper portion of the structure, while a reflectionmirror of the upper multilayer film reflection mirror 412 of the surfaceemitting laser exists in the lower portion of the structure.

That is, this means that a resonator is newly formed on the outermostsurface of the low reflection region in addition to the surface emittinglaser resonator. The resonance wavelength of the new resonator isobserved as the dip wavelength 514 due to the phase adjusting layer.

However, in this state as it is, the reflectance of the interfacebetween the air and the GaAs layer as the upper reflection mirror isgreatly different from the reflectance of the upper multilayer filmreflection mirror as the lower reflection mirror, and hence it isdifficult to clearly observe the resonance wavelength.

Thus, the reflectance at the resonance wavelength can be greatly reducedby introducing the absorption as the second condition. By forming thebroad dip, the value of the resonance wavelength of the dip can bepractically specified.

FIG. 5 shows two kinds of reflection spectra in a case (502) where noabsorption exists, and reflection spectra in a case (504) where smallabsorption (1000 cm⁻¹) exists.

In the case where no absorption or small absorption exists, thereduction in the dip can hardly be recognized, and hence the wavelengthcannot be clearly specified.

Further, as the absorption of a semiconductor, free carrier absorption,and the like, may occur. However, in the free carrier absorption, evenwhen a very high doping of about 1×10²⁰ cm⁻³ is used, the absorptioncoefficient of only about 1000 cm⁻¹ can be obtained. As a result, asufficient dip is not formed, and hence the object of the presentinvention cannot be sufficiently attained.

On the other hand, the absorption coefficient of the band-to-bandabsorption is generally in a range of 5000 cm⁻¹ or more, and hencesufficient dips are obtained as denoted by reference numerals 506, 508and 510 in FIG. 5, so as to enable the wavelength to be specified.

Meanwhile, this absorption layer is indispensable to specify the dipwavelength 514 due to the phase adjusting layer, but the absorptionlayer is not necessary as the surface emitting laser and may causedecrease in laser element characteristics.

Therefore, there are some desirable forms in the structure andarrangement of the absorption layer. First, the absorption layer isarranged on the surface side from the middle point in thickness of theupper multilayer film reflection mirror, on the side opposite to thesubstrate used for the crystal growth. It is preferred that theabsorption layer is formed within five pairs of layers on the surfaceside of the upper multilayer film reflection mirror.

This is because when the surface emitting laser functions to oscillatein the single fundamental transverse mode, the light distribution in thein-plane direction is concentrated on the high reflection region whereno phase adjusting layer exists, and the light distribution in the depthdirection is reduced toward the surface as denoted by reference numeral606 in FIG. 6.

On the other hand, when the reflection spectra of the low reflectionregion where a phase adjusting layer exists are measured, the lightdistribution is increased toward the outermost surface as denoted byreference numeral 608 in FIG. 6.

However, even in the low reflection region, the light distribution isgradually increased, as shown in FIG. 6, on the side near an activelayer (substrate) in the multilayer film reflection mirror.

Therefore, when the absorption layer is arranged on the side near thesurface in the multilayer film reflection mirror, the necessaryabsorption is increased at the time of reflection spectrum measurementso as to enable the resonance wavelength 514 to be clearly specified,while unnecessary absorption is reduced at the time of operation of thesurface emitting laser, so as to suppress the degradation of the elementcharacteristics.

Further, as shown in FIG. 6, it is preferred that in the uppermultilayer film reflection mirror, the absorption layer is arranged neara interface 610 from the high refractive index layer to the lowrefractive index layer, when seen from the surface.

In this case, as shown in FIG. 6, on the surface side of the multilayerfilm reflection mirror, an antinode is formed near the interface in thelow reflection region as shown by the light distribution 608, so thatthe absorption is increased. Thereby, the dip wavelength 514 can bemeasured more clearly in the reflection spectrum measurement.

On the other hand, a node of the light distribution 606 is formed nearthe interface in the high reflection region, so that the absorption canbe suppressed as much as possible and the influence of the absorptionlayer on the element characteristics can be minimized.

Further, it can be seen from FIG. 14 that the thickness of theabsorption layer needs to be set to at least 2 nm or more in order toenable the dip wavelength to be clearly observed.

On the other hand, when the thickness of the absorption layer isexcessively increased, unnecessary absorption is increased duringoperation of the element. Thus, it is preferred that the thickness ofthe absorption layer is set to be less than the half (about 30 nm) ofthe layer configuring the multilayer film reflection mirror.

Alternatively, it is also preferred to arrange the absorption layer inthe phase adjusting layer. This is because in the high reflection regionwhere the in-plane direction light distribution of the desiredfundamental transverse mode is concentrated, the phase adjusting layeris removed by being etched in a concave shape, and hence the light ishardly absorbed in the high reflection region at the time of operationof the element.

The layer thickness of the absorption layer in this case may be setcomparatively large because the absorption layer is removed. Further, inconsideration of the fact that the absorption layer is also used as acontact layer for an electrode, it is preferred that the layer thicknessof the absorption layer is set to 10 nm or more. It is more preferredthat the layer thickness of the absorption layer is set to 20 nm ormore.

Subsequently, in order to clarify the relationship between the dipwavelength and the introduced reflection loss, the variations wereassumed in the thickness of the layers configuring the phase adjustinglayer and the multilayer film reflection mirror, and the dip wavelengthand the loss were investigated in the case where such variations werecaused.

Specifically, the dip wavelength and the loss were investigated byassuming not only the case where the layer thickness of the phaseadjusting layer (604, first layer) as shown in FIG. 6 is varied, butalso the case where the layer thickness of all of the layers (612, 614and 616) configuring the multilayer film reflection mirror under thephase adjusting layer is varied.

That is, the case where the layer thickness of each of the second layer(612), the third layer (614), and the fourth layer (616) is separatelyvaried in the range of −20 to +20 nm from a target value (usually set tothe optical thickness of ¼ wavelength), was assumed as the case whichmay be caused in the crystal growth, and the like.

Then, there was investigated how the dip wavelength and the reflectionloss were changed in this case.

When each of the layers in FIG. 6 is made to specifically correspond tothe layers in FIG. 4, the first layer corresponds to the GaAs phaseadjusting layer 418 having the optical thickness of ¼ wavelength.

Further, the second layer corresponds to the Al_(0.5) 0.Ga₅As highrefractive index layer 416, and the third layer corresponds to theAl_(0.9)Ga_(0.1)As low refractive index layer 414.

Further, the fourth layer corresponds to the layer having the opticalthickness of ¼ wavelength (Al_(0.5)Ga_(0.5)As high refractive indexlayer) existing under the third layer.

FIG. 7 illustrates the change of the loss introduced when the thicknessof each of the layers is varied.

Here, there was used, as a loss, a value (normalized loss) normalized bythe loss value in the high reflection region 202.

From this figure, it was seen that not only when the thickness of thephase adjusting layer as the first layer is varied but also when thethickness of the second, third, or fourth layer that exists under thefirst layer is varied, the loss introduced according to the variationamount is almost similarly changed.

In other words, this means that highly precise control of only thethickness of the phase adjusting layer is not sufficient to control theintroduced loss.

From this investigation, it was found that it is necessary to controlthe thickness of the whole layers including the phase adjusting layerand the layers which exist under the phase adjusting layer and whichconfigure the multilayer film reflection mirror.

Subsequently, there was also investigated here a relationship betweenthe shift in the dip wavelength in the low reflection region, whichshift is caused by the phase adjusting layer, and the introduced loss inthe case where the thickness of each of the four layers is separatelyvaried as described above.

Here, the shift in the dip wavelength means a shift from the referenceset to the dip wavelength in the case where the phase adjusting layerhas the optical thickness of ¼ wavelength.

FIG. 8 illustrates the obtained relationship.

The horizontal axis represents the shift in the dip wavelength and thevertical axis represents the loss normalized similarly to FIG. 7.

As a result, it can be seen that even when not only the thickness of thephase adjusting layer as the first layer but also the thickness of thesecond, third or fourth layer, which exists under the first layer, arevaried, the dip wavelength is shifted by the amount corresponding to thevaried amount of each of the layers, and the loss is reduced almostsimilarly according to the shift of the dip wavelength.

In other words, it was found that as long as only the shift in the dipwavelength was grasped, the introduced loss could be quantitativelyestimated without the need to precisely grasp the variation amount ofeach of the layers.

Further, it can be seen from the figure that a necessary loss can beobtained by adjusting, for example, the thickness of the phase adjustinglayer so as to make the dip wavelength become a value corresponding tothe loss.

Here, description is given by taking as an example the red surfaceemitting laser, and hence the GaAs layer is taken as an example of theabsorption layer. However, any layer may be used as long as the layerexhibits a sufficient absorption performance at the oscillationwavelength.

For example, AlGaAs, AlGaAsP, InGaAsP, InGaAs, and the like are listedfor a red surface emitting laser having a wavelength of 680 nm. There islisted InGaAs for a surface emitting laser having a wavelength band of850 to 980 nm.

Further, for a ZnSe based surface emitting laser having a shorterwavelength, there are listed MgZnCdSSeTe, ZnCdSe, and the like. For aGaN based surface emitting laser, there are listed AlGaInNPAs, InGaN,and the like.

Next, there will be specifically described a manufacturing procedure ofa surface relief structure using this principle.

First, a necessary loss value in the low reflection region is determinedin order to obtain desired element characteristics.

There are calculated a layer thickness corresponding to the loss and adip wavelength in the low reflection region in the case of the loss.

For example, when a normalized loss of 5 in FIG. 8 is necessary, theshift from the dip wavelength in the low reflection region in the casewhere each of the layers of the region is formed to have the layerthickness equivalent to the optical thickness of ¼ wavelength, is set to0 nm as the target value of the dip wavelength.

On the other hand, when a normalized loss of 4 is necessary, thewavelength shift from the dip wavelength in the low reflection region inthe case where each of the layers of the region is formed to have thelayer thickness equivalent to the optical thickness of ¼ wavelength, isset to −4 nm or +5 nm as the target value of the dip wavelength.

At the time when the phase adjusting layer as the final layer iscrystally grown, the reflection spectra is measured, so as to checkwhether or not the shift of the dip wavelength is set to the abovedescribed desired value.

When the shift is not sufficient, crystal growth is performed again,while when the shift is excessive, the adjustment is performed byetching, and the like.

In this way, the crystal growth may be performed again after themeasurement of the reflection spectra, and hence it is preferred thatthe outermost surface of the wafer is terminated by a layer notcontaining Al.

Alternatively, by performing in situ observation of the reflectionspectra during the crystal growth, the crystal growth may be ended atthe time when a desired dip wavelength is obtained.

In this case, it is not necessary to take out the wafer from the crystalgrowing apparatus, and hence the outermost surface of the wafer need notnecessarily be terminated by a layer not containing Al.

Next, there will be described the formation of a relief structure in thewafer in which the amount of the introduced loss is controlled asdescribed above.

A concave relief as shown in FIG. 2A is formed by removing the phaseadjusting layer presently existing at the outermost surface by using dryor wet etching.

As shown in FIG. 3, the allowable layer thickness, at which the highreflectance (low loss region) can be obtained, has conversely a widerange (±15 nm), and hence the controllability required for the abovedescribed etching is low.

On the other hand, the selective etching using an etching-stop layer mayalso be used in order to further improve the reproducibility anduniformity.

Here, specifically, only the GaAs layer as the final layer may be etchedselectively with respect to the Al_(0.5)Ga_(0.5)As high refractive indexlayer that exists under the GaAs layer, and the etching depth can becontrolled by using a citric acid based etchant without the influence oftime.

A highly precise relief can be formed by performing the above describedprocedure, and thereby an element having excellent reproducibility anduniformity can be formed.

According to the manufacturing method of the above described exemplaryembodiment, a concave surface relief structure can be manufactured withgood precision, but the material used for the manufacture of the surfacerelief structure is not limited to the AlGaAs based semiconductormaterial.

For example, various semiconductor materials, such as other III-V groupcompound semiconductors or II-VI group compound semiconductors, can beused.

Further, the above described structure of the present exemplaryembodiment can also be applied to a relief structure using othermaterials, such as a dielectric material and a metallic material.

Further, in the above, description is given by taking as an example asurface emitting laser structure, but the principle according to thepresent invention is not limited to the surface emitting laser. Theprinciple according to the present invention can be applied to a lightemitting and receiving element using a general multilayer filmreflection mirror.

Exemplary Embodiments

In the following, there will be described exemplary embodimentsaccording to the present invention.

Exemplary embodiment 1

As exemplary embodiment 1, there will be described a configurationexample of a vertical cavity surface emitting laser including a concavesurface relief structure and oscillating at 680 nm, and a manufacturingmethod of the surface emitting laser.

FIG. 1 is a cross-sectional schematic view for describing aconfiguration example of a vertical cavity surface emitting laser in thepresent exemplary embodiment.

In FIG. 1, reference numeral 102 denotes an n-side electrode, referencenumeral 104 denotes an n-type GaAs substrate, reference numeral 106denotes an n-type AlAs/Al_(0.5)Ga_(0.5)As multilayer film reflectionmirror, reference numeral 108 denotes an n-type AlGaInP spacer layer,and reference numeral 110 denotes a GaInP quantum well active layer.

Reference numeral 112 denotes a p-type AlGaInP spacer layer, referencenumeral 114 denotes a p-type Al_(0.9)Ga_(0.1)As/Al_(0.5)Ga_(0.5)Asmultilayer film reflection mirror, and reference numeral 116 denotes aAl_(0.98)Ga_(0.02)As oxidization constriction layer.

Reference numeral 118 denotes a p-type Al_(0.9)Ga_(0.1)As low refractiveindex layer, and reference numeral 120 denotes a p-typeAl_(0.5)Ga_(0.5)As high refractive index layer.

Reference numeral 122 denotes a phase adjusting layer, and here, a GaAslayer is used as the phase adjusting layer.

Further, high concentration p-type doping of 5×10¹⁹ cm⁻³ or more isperformed to this layer in order to enable the layer to also function asa contact layer. Reference numeral 124 denotes an insulating film, andreference numeral 126 denotes a p side electrode.

In the present exemplary embodiment, the active layer 110 has a multiplequantum well structure which is configured by a plurality of GaInPquantum well layers and a plurality of Al_(0.25)Ga_(0.25)In_(0.5)Pbarrier layers. The layer thickness of the p-type AlGaInP spacer layer108 and the p-type AlGaInP spacer layer 112 is adjusted so that themultiple quantum well structure is located at an antinode of an internallight standing wave. As a resonator configured by these layers andhaving an oscillation wavelength of 680 nm, the layer thickness of thelayers is adjusted to become an integer multiple of the oscillationwavelength. The active layer itself is adjusted and manufactured so asto have an emission peak wavelength (for example, 660 to 670 nm) whichis set on the shorter wavelength side of the resonance wavelength of thesurface emitting laser resonator.

The n-type multilayer film reflection mirror 106 is configured bylaminating 60 pairs of an n-type AlAs low refractive index layer and ann-type Al_(0.5)Ga_(0.5)As high refractive index layer, each of whichlayer has an optical thickness of ¼ oscillation wavelength of 680 nm.

The center wavelength of the reflection band of this reflection mirroris adjusted to 680 nm which is the oscillation wavelength. Si and Se aredoped in order to obtain n-type conductivity.

In order to further lower the electric resistance, there may also beused a method, such as a method of providing a composition inclinedlayer between two layers having different refractive indexes, and amethod of using a modulation doping in which the doping amount isreduced around an antinode of the light distribution to lower theelectric resistance while reducing the optical absorption, and in whichthe doping amount is increased around a node of the light distribution.

The P-type multilayer film reflection mirror 114 is configured bylaminating 38 pairs of the p-type Al_(0.9)Ga_(0.1)As low refractiveindex layer 118 and the p-type Al_(0.5)Ga_(0.5)As high refractive indexlayer 120, each of which layer has the optical thickness of ¼ wavelengthof 680 nm.

The center wavelength of the reflection band of this reflection mirroris adjusted to 680 nm which is the oscillation wavelength. C and Zn aredoped in order to obtain p-type conductivity. In order to further lowerthe electric resistance, such a method as is used for the n-typemultilayer film reflection mirror can be applied also to the p-typereflection mirror.

One of the p-type Al_(0.9)Ga_(0.1)As low refractive index layers 118near the active layer in the p-type multilayer film reflection mirror isreplaced by the p-type Al_(0.98)Ga_(0.02)As oxidization constrictionlayer 116. This layer is selectively oxidized under a high temperaturesteam atmosphere, so as to be insulated from the peripheral portion ofthe element, and thereby a current constriction structure which allowscurrent to flow only through the central portion thereof is formed.

In the present exemplary embodiment, the region in which current isallowed to flow by the oxidization constriction was adjusted to analmost circular shape having a diameter of 6 μm.

Usually, the p-type multilayer film reflection mirror 114 is terminatedby the high refractive index layer 120 having the optical thickness of ¼wavelength.

In the present exemplary embodiment, in order to realize a singlefundamental transverse mode oscillation, the light emitting centralportion is terminated as usual by the high refractive index layer 120 sothat high reflectance necessary for the oscillation can be obtained. Inthis case, the phase adjusting layer 122 is further added onto the highrefractive index layer 120 in the light emitting peripheral portion sothat the low reflectance enough to prevent the high order modeoscillation can be obtained.

Next, there will be described in detail an example of a manufacturingmethod of the vertical cavity surface emitting laser in the presentexemplary embodiment.

The structure of the vertical cavity surface emitting laser is the sameas the structure as described above, and is manufactured by thefollowing processes.

First, in the first process, the layer thickness of the phase adjustinglayer is determined.

Next, in the second process, the absorption layer is determined.

Next, in the third process, the dip wavelength due to the phaseadjusting layer is calculated.

Next, in the fourth process, after the phase adjusting layer is grown,the reflection spectra are measured and then compared with thecalculation value of the dip wavelength obtained in the third process.The layer thickness of the phase adjusting layer is adjusted until theactually measured value of the dip wavelength coincides with thecalculation value.

Next, in the fifth process, an element is formed by using the wafersubjected to the above described adjustment.

In the following, there will be described in more detail each of theabove described processes in order.

In the first process, there is determined the layer thickness of thephase adjusting layer which causes a loss necessary to realize thesingle mode oscillation.

In the present exemplary embodiment, there was selected the GaAs layerhaving the optical thickness of ¼ wavelength (in this case 45 nm) as thelayer thickness which allows the normalized loss of 5 as illustrated inFIG. 8 to be obtained.

Here, the optical thickness of ¼ wavelength was selected. However,according to required element characteristics, a layer thicknesscorresponding to a necessary loss may be determined, for example, byreferring to FIG. 7.

In the second process, an band-to-band absorption layer is arranged inthe phase adjusting layer or the upper multilayer film reflection mirrorso as to enable the dip wavelength to be measured with good precision.More preferably, the band-to-band absorption layer may be arranged inthe form as described above.

Further, in order to form the high reflection region with goodprecision, it is preferred to configure such that the phase adjustinglayer 122 can be etched selectively with respect to the p-typeAl_(0.5)Ga_(0.5)As high refractive index layer 120.

As an example of a structure satisfying the above, the GaAs layerserving as the absorption layer for the oscillation wavelength of 680 nmwas selected, so as to be arranged in the whole phase adjusting layer.

The phase adjusting layer made of GaAs can be selectively etched byusing a citric acid based etchant, and the like, with respect to theAl_(0.5)Ga_(0.5)As high refractive index layer 120 in the multilayerfilm reflection mirror.

In the third process, there is calculated the reflection spectra in thestructure in which all the layers up to the phase adjusting layer areformed.

FIG. 10 illustrates the calculation result. Here, there are illustratedthe changes in the reflection spectra in the case where the layerthickness of the phase adjusting layer is intentionally changed in arange from −10 nm to +10 nm at every 5 nm based on the target value of45 nm that is the optical thickness of ¼ wavelength.

In the multilayer film reflection mirror reflection band spectra, thereis clearly observed a large dip which is significantly different fromthe reflection spectra of the conventional surface emitting laser wafer,and which is greatly influenced by the resonator formed by the phaseadjusting layer including the absorption layer.

When the thickness of the phase adjusting layer is changed, the dipwavelength is changed according to the change in the thickness. When themeasurement resolution of the dip wavelength is set in the range ofseveral nm, the variation in the layer thickness is also suppressedwithin the range of ±5 nm, so that a desired loss can be introduced.

In the fourth process, the reflection spectra of the manufactured waferare measured.

FIGS. 11A and 11B illustrate the actually measured results.

FIG. 11A illustrates the measured result of reflection spectra of thewafer which was manufactured by actually aiming at 45 nm of the layerthickness of the phase adjusting layer and in which the crystal growthwas once stopped after the formation of the phase adjusting layer.

From the comparison between the measured results in FIG. 11A and FIG.10, it is seen that the dip wavelength in FIG. 11 appears in the shortwavelength side from the dip wavelength in the case of the opticalthickness of ¼ wavelength.

This means that, in spite of 45 nm of the layer thickness actuallytargeted as the layer thickness of the phase adjusting layer, themeasured layer thickness is identified to be 37.5 nm, which is smallerby about 7.5 nm than the target layer thickness, because the layer wasgrown at a lower growth rate than estimated due to low temperaturegrowth or etch back by high concentration C doping.

Then, a layer of 7.5 nm was added to the wafer.

The added layers is the GaAs layer which is the same as the layerexisting at the uppermost surface and doped with high concentration C.The layer was added by crystal growth.

FIG. 11B illustrates the measurement result of the reflection spectrumof the wafer. From the similar comparison between the measured resultsin FIG. 11B and FIG. 10, it can be estimated that, in FIG. 11B, thelayer thickness is set to about 45 nm as adjusted.

In this way, according to the method of the present exemplaryembodiment, the loss can be controlled in extremely high precision basedon the dip wavelength obtained by the reflection spectrum measurement.

In the fifth process, the element formation is performed by using thewafer subjected to the layer thickness adjustment of the final layer,here by using the wafer in FIG. 11B.

First, the surface relief is formed. As the mask pattern forming processfor forming the relief, a dielectric layer is deposited, and SiO₂ ispatterned by using photo lithography and wet etching using bufferedfluoric acid.

Subsequently, the GaAs phase adjusting layer 122 is selectively etchedby using citric acid based etchant with respect to theAl_(0.5)Ga_(0.5)As high refractive index layer 120, so that a concaverelief having a diameter of φ3.5 μm is formed.

Next, a mesa having a diameter of 20 to 30 μm is formed. Similarly tothe above, the dielectric layer is patterned again and etched by dryetching, and the like, until at least the side surface of the AlGaAsselective oxidation layer is exposed.

At this time, alignment is performed with care to make the center of therelief diameter match with the center of the mesa diameter.Alternatively, there may also be adopted a process which enables theself-alignment of the centers.

Then, the Al_(0.98)Ga_(0.02)As oxidization constriction layer 116 isoxidized from the periphery of the mesa as required under hightemperature steam atmosphere.

Here, the oxidation time is adjusted so that there is formed anoxidation constriction region which allows current to flow in thecentral region of a diameter of 6 μm. Then, a necessary dielectric layeris deposited and patterned again, so as to expose a portion of thep-type GaAs contact layer, on which portion a ring shaped Ti/Au isvapor-deposited so as to be formed as the p side electrode.

Then, AuGe/Ni/Au is vapor-deposited on the rear surface of the n-typeGaAs substrate and annealed at about 400° C., so that the n sideelectrode is formed.

Finally, a chip of a necessary size is cut from the wafer. The chip isdie-bonded to a package and the p side electrode is wire bonded, so thatan element is completed.

Further, when the mask for an array is suitably designed, it is possibleto manufacture not only a single element but also an array in which aplurality of elements are two dimensionally arranged. In this way, theadvantage of the surface emitting laser is that an array structure canbe obtained comparatively easily only by changing the mask.

According to the above described configuration of the present exemplaryembodiment, the reproducibility of the amount of introduced loss issignificantly improved by the reflection spectrum measurement, so thatthe reproducibility and uniformity between wafers can be significantlyimproved.

Exemplary Embodiment 2

As exemplary embodiment 2, there is described a vertical cavity surfaceemitting laser which includes a concave surface relief structure andsimilarly oscillates at 680 nm.

FIG. 9 is a cross-sectional schematic view for describing aconfiguration example of a vertical cavity surface emitting laser in thepresent exemplary embodiment.

In FIG. 9, the same portions as those illustrated in FIG. 1 are denotedby the same reference numerals. Thus, the description of the sameportions is omitted, and only different portions are described.

In FIG. 9, reference numeral 902 denotes a phase adjusting layer, andreference numeral 904 denotes a GaAs absorption layer.

In the present exemplary embodiment, here, a GaAs contact layer having athickness of 20 nm and an Al_(0.9)Ga_(0.1)As low refractive index layerhaving a thickness of 27 nm are used in the phase adjusting layer 902.The phase adjusting layer 902 is set to have a thickness justcorresponding to an optical thickness of ¼ wavelength.

The light having the oscillation wavelength of 680 nm is also absorbedin the phase adjusting layer 902. However, in order to enable theabsorption to be more surely caused, the GaAs absorption layer 904having a thickness of 10 nm was arranged at the interface between theAl_(0.5)Ga_(0.5)As high refractive index layer 120 having a thickness of44 nm and the Al_(0.9)Ga_(0.1)As low refractive index layer 118 having athickness of 48 nm.

The interface corresponds to the interface 610 from the high refractiveindex layer to the low refractive index layer illustrated in FIG. 6.

Therefore, it is configured such that the total thickness of 44 nm ofthe thickness of the Al_(0.5)Ga_(0.5)As high refractive index layer 120,and 5 nm of the thickness which is half the thickness of the GaAsabsorption layer 902 having the thickness of 10 nm, corresponds to theoptical thickness of ¼ wavelength, while the total thickness of 5 nm ofthe thickness which is the remaining half of the thickness of the GaAsabsorption layer 902, and 48 nm of the thickness of theAl_(0.9)Ga_(0.1)As low refractive index layer 118, corresponds to theoptical thickness of ¼ wavelength.

The position of the node at which the GaAs absorption layer 902 isprovided becomes, as shown in FIG. 6, an antinode in the light intensitydistribution obtained in the reflection spectrum measurement in the lowreflection region. Thereby, a sufficient absorption is caused so thatthe measurement of the dip wavelength can be performed.

By using the structure according to the present exemplary embodiment, itis possible to estimate the amount of the loss introduced by the methodas described in exemplary embodiment 1, so that an element havingexcellent uniformity and reproducibility can be formed.

Exemplary Embodiment 3

As exemplary embodiment 3, there will be described a vertical cavitysurface emitting laser which includes a concave surface relief structureand which oscillates at a wavelength of 980 nm.

FIG. 13 is a cross-sectional schematic view for describing aconfiguration example of a vertical cavity surface emitting laser in thepresent exemplary embodiment.

In FIG. 13, the same portions as those illustrated in FIG. 1 are denotedby the same reference numerals. Thus, the description of the sameportions is omitted, and only different portions are described.

In FIG. 13, reference numeral 1306 denotes an n-typeAl_(0.9)Ga_(0.1)As/GaAs multilayer film reflection mirror, referencenumeral 1308 denotes an n-type AlGaAs spacer layer, and referencenumeral 1310 denotes an InGaAs quantum well active layer. Referencenumeral 1312 denotes a p-type AlGaAs spacer layer, reference numeral1314 denotes a p-type Al_(0.9)Ga_(0.1)As/GaAs multilayer film reflectionmirror, and reference numeral 1320 denotes a p-type GaAs high refractiveindex layer. Further, reference numeral 1322 denotes a phase adjustinglayer in which there are used here a GaAs layer and anIn_(0.3)Ga_(0.7)As layer 1328 for absorption.

In the present exemplary embodiment, the active layer 1310 has amultiple quantum well structure configured by a plurality ofIn_(0.2)Ga_(0.8)As quantum well layers and GaAs barrier layers.

The layer thickness of the n-type AlGaAs spacer layer 1308 and thep-type AlGaAs spacer layer 1312 is adjusted so as to allow the multiplequantum well to be located at an antinode of the internal light standingwave.

As a resonator configured by these layers, the thickness of the layersis adjusted so as to have an optical thickness of an integer multiple ofthe oscillation wavelength of 980 nm. The active layer is adjusted andmanufactured so that the wavelength of light emitted from the activelayer itself has a light emission peak wavelength in the range of 960 to970 nm.

The phase adjusting layer 1322, whose total layer thickness is set to 80nm that corresponds to an optical thickness of ¼ wavelength, isconfigured by successively providing, from the outermost surface, a GaAslayer having a thickness of 20 nm, an In_(0.3)Ga_(0.7)As having athickness of 5 nm, and a GaAs layer having a thickness of 55 nm.

The phase adjusting layer 1322 also serves as the contact layer andhence is highly doped at 5×10¹⁹ cm⁻³ or more. Here, theIn_(0.3)Ga_(0.7)As layer having the above described arrangement andlayer thickness serves as an band-to-band absorption layer for the lightemission wavelength of 980 nm, so that the dip wavelength due to thephase adjusting layer can be clearly observed in the reflection spectra.

By using the above described structure according to the presentexemplary embodiment, it is possible to estimate the amount of the lossintroduced by the method as described in exemplary embodiment 1, so thatan element having high uniformity and reproducibility can be formed.

Exemplary Embodiment 4

As exemplary embodiment 4, there will be described a configurationexample of an optical apparatus configured by applying the verticalcavity surface emitting laser according to the present invention.

Here, there is described a configuration example of an image formingapparatus configured by using as an optical apparatus the red surfaceemitting laser array using the vertical cavity surface emitting lasersaccording to the present invention. FIGS. 12A and 12B are figuresillustrating a configuration of an electrophotographic recording typeimage forming apparatus in which a laser array using the red surfaceemitting lasers according to the present exemplary embodiment ismounted.

FIG. 12A is a top view of the image forming apparatus, and FIG. 12B is aside view of the image forming apparatus. In FIGS. 12A and 12B,reference numeral 1200 denotes a photoreceptor, reference numeral 1202denotes a charger, reference numeral 1204 denotes a developing device,reference numeral 1206 denotes a transfer charger, reference numeral1208 denotes a fixing device, reference numeral 1210 denotes a rotarypolygon mirror, and reference numeral 1212 denotes a motor. Further,reference numeral 1214 denotes a red surface emitting laser array,reference numeral 1216 denotes a reflection mirror, reference numeral1220 denotes a collimator lens, and reference numeral 1222 denotes anf-θ lens.

The image forming apparatus according to the present exemplaryembodiment is configured such that light beams from the light sourceconfigured by applying the vertical cavity surface emitting lasersaccording to the present invention are made incident on thephotoreceptor so as to form an image.

Specifically, the motor 1212 illustrated in FIGS. 12A and 12B isconfigured so as to rotationally drive the rotary polygon mirror 1210.

Further, the rotary polygon mirror 1210 in the present exemplaryembodiment includes six reflection surfaces. Reference numeral 1214denotes the red surface emitting laser array serving as a light sourcefor recording.

The red surface emitting laser array 1214 is turned on and off by alaser driver (not illustrated) according to an image signal. The laserlight beam modulated in this way is irradiated from the red surfaceemitting laser array 1214 toward the rotary polygon mirror 1210 via thecollimator lens 1220.

The rotary polygon mirror 1210 is rotated in the arrow direction. Thelaser light beams output from the red surface emitting laser array 1214are reflected to be deflected beams whose emission angle is continuouslychanged by the reflection surface of the rotary polygon mirror 1210according to the rotation of the rotary polygon mirror 1210.

The reflected light beams are subjected to distortion aberrationcorrection, and the like, by the f-θ lens 1222, and are then irradiatedonto the photoreceptor 1200 through the reflection mirror 1216, so as tobe scanned in the main scanning direction on the photoreceptor 1200.

At this time, images of a plurality of lines corresponding to the redsurface emitting laser array 1214 are formed in the main scanningdirection of the photoreceptor 1200 by the light beams reflected by onereflection surface of the rotary polygon mirror 1210.

In the present exemplary embodiment, a 4×8 red surface emitting laserarray 1214 is used, and hence images of 32 lines are simultaneouslyformed.

The photoreceptor 1200 is charged beforehand by the charger 1202, and issuccessively exposed by the scanning of the laser light beam, so that anelectrostatic latent image is formed.

Further, the photoreceptor 1200 is rotated in the arrow direction, andthe formed electrostatic latent image is developed by the developingdevice 1204. The developed visible image is transferred onto a transferpaper (not shown) by the transfer charger 1206.

The transfer paper with the visible image transferred thereon isconveyed to the fixing device 1208, so as to be fixed, and is thendischarged outside the image forming apparatus.

Further, in the present example, the 4×8 red surface emitting laserarray is used, but the red surface emitting laser array is not limitedto this. An m×n red surface emitting laser array (where m and n arenatural numbers) may be used.

As described above, when the red surface emitting laser array accordingto the present exemplary embodiment is used in an electrophotographicrecording type image forming apparatus, it is possible to obtain animage forming apparatus which enables high speed and highly preciseprinting.

Note that in the above description, there is described an example inwhich an image forming apparatus is configured as an optical apparatus,but the present invention is not limited to such configuration.

For example, an optical apparatus, such as a projection display, mayalso be configured such that a light source configured by applying thevertical cavity surface emitting laser according to the presentinvention is used, and that the light beam from the light source is madeincident on an image display body so as to display an image.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2008-199000, filed Jul. 31, 2008, which is hereby incorporated byreference herein in its entirety.

1. A surface emitting laser which is configured by laminating on a substrate a lower reflection mirror, an active layer, and an upper reflection mirror, which includes, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, wherein the upper reflection mirror is configured by a multilayer film reflection mirror based on a laminated structure formed by laminating a plurality of layers, the multilayer film reflection mirror includes a phase adjusting layer which has an optical thickness in the range of λ/8 to 3λ/8 inclusive in a light emitting peripheral portion on the multilayer film reflection mirror, and an absorption layer causing band-to-band absorption is provided in the phase adjusting layer.
 2. The surface emitting laser according to claim 1, wherein the absorption coefficient of the absorption layer is set to 5000 cm⁻¹ or more for the wavelength λ.
 3. The surface emitting laser according to claim 1, wherein the absorption layer is arranged at a layer positioned at the middle point in a thickness direction of the phase adjusting layer, or arranged on the surface side from the layer positioned at the middle point in the thickness direction of the phase adjusting layer.
 4. An optical apparatus comprising, as a light source, a surface emitting laser array configured by arranging a plurality of the surface emitting lasers according to claim
 1. 5. A surface emitting laser which is configured by laminating on a substrate a lower reflection mirror, an active layer, and an upper reflection mirror, which includes, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, wherein the upper reflection mirror is configured by a multilayer film reflection mirror based on a laminated structure formed by laminating a plurality of layers, the multilayer film reflection mirror includes a phase adjusting layer which has an optical thickness in the range of λ/8 to 3λ/8 in a light emitting peripheral portion on the multilayer film reflection mirror, and an absorption layer causing band-to-band absorption is provided on the surface side from a layer laminated at the middle point in thickness of the laminated structure that configures the multilayer film reflection mirror.
 6. The surface emitting laser according to claim 5, wherein the absorption coefficient of the absorption layer is 5000 cm⁻¹ or more for the wavelength λ.
 7. The surface emitting laser according to claim 5, wherein the absorption layer is provided within five pairs of layers from the surface side of the laminated structure.
 8. The surface emitting laser according to claim 5, wherein the absorption layer is arranged so that when seen from the surface side of the multilayer film reflection mirror, a part of the absorption layer is included in the interface from a high refractive index layer to a low refractive index layer in the multilayer film reflection mirror.
 9. An optical apparatus comprising, as a light source, a surface emitting laser array configured by arranging a plurality of the surface emitting lasers according to claim
 5. 10. A surface emitting laser which is configured by laminating on a substrate a lower reflection mirror, an active layer, and an upper reflection mirror, which includes, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, wherein the upper reflection mirror is configured by a multilayer film reflection mirror based on a laminated structure formed by laminating a plurality of layers, the multilayer film reflection mirror includes a phase adjusting layer which has an optical thickness in the range of λ/8 to 3λ/8 in a light emitting peripheral portion on the multilayer film reflection mirror, and an absorption layer having an absorption coefficient of 5000 cm⁻¹ or more for the wavelength λ is provided in the phase adjusting layer.
 11. A surface emitting laser which is configured by laminating on a substrate a lower reflection mirror, an active layer, and an upper reflection mirror, which includes, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, wherein the upper reflection mirror is configured by a multilayer film reflection mirror based on a laminated structure formed by laminating a plurality of layers, the multilayer film reflection mirror includes a phase adjusting layer which has an optical thickness in the range of λ/8 to 3λ/8 in a light emitting peripheral portion on the multilayer film reflection mirror, and an absorption layer having an absorption coefficient of 5000 cm⁻¹ or more for the wavelength λ is provided on the surface side from a layer laminated at the middle point in thickness of the laminated structure that configures the multilayer film reflection mirror.
 12. A manufacturing method of a surface emitting laser in which a lower reflection mirror, an active layer, and an upper reflection mirror are successively laminated on a substrate, in which there is formed, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, the manufacturing method comprising: forming, as the upper reflection mirror, a multilayer film reflection mirror based on a laminated structure; forming, on the multilayer film reflection mirror, a phase adjusting layer which is for reducing the reflectance and which includes an absorption layer causing band-to-band absorption; measuring reflection spectra by irradiating the surface of the phase adjusting layer with light; measuring a broad dip wavelength obtained by measuring the reflection spectra; and adjusting the thickness of the phase adjusting layer based on the dip wavelength.
 13. The manufacturing method of the surface emitting laser according to claim 12, wherein the absorption coefficient of the absorption layer is set to 5000 cm⁻¹ or more for the wavelength λ.
 14. The manufacturing method of the surface emitting laser according to claim 12, further comprising forming, when the absorption layer is formed, the absorption layer at a layer positioned at the middle point in a thickness direction of the phase adjusting layer, or on the surface side from the layer positioned at the middle point in the thickness direction of the phase adjusting layer.
 15. A manufacturing method of a surface emitting laser in which a lower reflection mirror, an active layer, and an upper reflection mirror are successively laminated on a substrate, in which there is formed, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, the manufacturing method comprising: forming, when a multilayer film reflection mirror based on a laminated structure is formed as the upper reflection mirror, an absorption layer causing band-to-band absorption on the surface side in the laminated structure from a layer laminated at the middle point in thickness of the laminated structure; measuring reflection spectra by irradiating the laminated structure with light; measuring a broad dip wavelength obtained by measuring the reflection spectra; forming, after the multilayer film reflection mirror as the upper reflection mirror is formed, a phase adjusting layer for reducing reflectance on the multilayer film reflection mirror; and adjusting the thickness of the phase adjusting layer based on the dip wavelength.
 16. The manufacturing method of the surface emitting laser according to claim 15, wherein the absorption coefficient of the absorption layer is set to 5000 cm⁻¹ or more for the wavelength λ.
 17. The manufacturing method of the surface emitting laser according to claim 15, further comprising forming, when the absorption layer is formed, the absorption layer within five pairs of layers from the surface side of the laminated structure.
 18. The manufacturing method of the surface emitting laser according to claim 15, further comprising forming, when the absorption layer is formed, the absorption layer so that when seen from the surface side of the multilayer film reflection mirror, a part of the absorption layer is included in the interface from a high refractive index layer to a low refractive index layer in the multilayer film reflection mirror.
 19. The manufacturing method of the surface emitting laser according to claim 15, further comprising forming, when the absorption layer is formed, the absorption layer so that the thickness of the absorption layer is set to 2 nm or more to 30 nm or less.
 20. A manufacturing method of a surface emitting laser in which a lower reflection mirror, an active layer, and an upper reflection mirror are successively laminated on a substrate, in which there is formed, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, the manufacturing method comprising: forming, as the upper reflection mirror, a multilayer film reflection mirror based on a laminated structure; forming, on the multilayer film reflection mirror, a phase adjusting layer which is for reducing the reflectance and which includes an absorption layer having an absorption coefficient of 5000 cm⁻¹ or more for the wavelength λ; measuring reflection spectra by irradiating the surface of the phase adjusting layer with light; measuring a broad dip wavelength obtained by measuring the reflection spectra; and adjusting the thickness of the phase adjusting layer based on the dip wavelength.
 21. A manufacturing method of a surface emitting laser in which a lower reflection mirror, an active layer, and an upper reflection mirror are successively laminated on a substrate, in which there is formed, in a light emitting section of the upper reflection mirror, a structure for controlling reflectance that is configured by a low reflectance region and a concave high reflectance region formed in the central portion of the low reflectance region, and which oscillates at a wavelength of λ, the manufacturing method comprising: forming, when a multilayer film reflection mirror based on a laminated structure is formed as the upper reflection mirror, an absorption layer having an absorption coefficient of 5000 cm⁻¹ or more for the wavelength λ on the surface side in the laminated structure from a layer laminated at the middle point in thickness of the laminated structure; measuring reflection spectra by irradiating the laminated structure with light; measuring a broad dip wavelength obtained by measuring the reflection spectra; forming, after the multilayer film reflection mirror as the upper reflection mirror is formed, a phase adjusting layer for reducing reflectance on the multilayer film reflection mirror; and adjusting the thickness of the phase adjusting layer based on the dip wavelength. 